Hi, apologies for the slightly long post, I'm hoping someone could hopefully point me in the right direction here. I'm trying to perform the FFT of a 100Khz signal using the STM32 Discovery board but I'm relatively new to the STM32 DSP in general. I've read up on a few things over the past few weeks and I've been trying to get a basic implementation working. Additionally, I've been following the basic working example here as well and adapted it to the F7 board. My main issue seems to fall into two parts:
- Implementing the delay for my given Frequency
- And Using DMA to fill the buffer with no empty values in the buffer.
My main code looks like this:
#include "main.h"
#include "stm32f7xx_hal.h"
#include <math.h>
#include "arm_math.h"
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#define FFT_INVERSE_FLAG ((uint8_t)0)
#define FFT_Normal_OUTPUT_FLAG ((uint8_t)1)
#define SAMPLES 2048
#define FFT_Length 1024
uint16_t uhADCxConvertedValue;
uint16_t index_fill_adc_buffer = 0;
float32_t FFT_Input_f32[FFT_Length*2];
float32_t FFT_Output_f32[FFT_Length];
uint16_t index_input_buffer = 0;
float32_t FFT_Input_f32[FFT_Length*2];
float32_t FFT_Output_f32[FFT_Length];
ADC_HandleTypeDef hadc1;
TIM_HandleTypeDef htim1;
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_DMA_Init(void);
static void MX_ADC1_Init(void);
static void MX_TIM1_Init(void);
int main(void)
{
SCB_EnableICache();
SCB_EnableDCache();
/* MCU Configuration----------------------------------------------------------*/
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */
HAL_Init();
SystemClock_Config();
MX_GPIO_Init();
MX_DMA_Init();
MX_ADC1_Init();
MX_USART1_UART_Init();
MX_TIM1_Init();
HAL_ADC_Start_DMA(&hadc1, (uint32_t*)&uhADCxConvertedValue, 1);
while (1)
{
// the ARM CFFT Module Struct
arm_cfft_radix4_instance_f32 FFT_struct;
// Fill FFT input buffer with the required data from ADCConvertedValue
for(index_input_buffer = 0; index_input_buffer < FFT_Length * 2; index_input_buffer+=2)
{
HAL_TIM_Base_Start(&htim1); // Call Delay
FFT_Input_f32[(uint16_t) index_input_buffer] = (float32_t)uhADCxConvertedValue / (float32_t) 4096.0;
// Imaginary Part
FFT_Input_f32[(uint16_t)(index_input_buffer + 1)] = 0;
}
// Initialise CFFT MOdule, set intFlag = 0, and doBitReverse = 1
// Watch Eli Hughes ARM CMSIS DSP video for explanation
arm_cfft_radix4_init_f32(&FFT_struct, FFT_Length, FFT_INVERSE_FLAG, FFT_Normal_OUTPUT_FLAG);
// Then process data through the CFFT/CIFFT Module
arm_cfft_radix4_f32(&FFT_struct, FFT_Input_f32);
/* Process the data through the Complex Magniture Module for calculating the magnitude at each bin */
arm_cmplx_mag_f32(FFT_Input_f32, FFT_Output_f32, FFT_Length);
// Remove DC Offset
FFT_Output_f32[0] = 0;
// Calculate Max value and return the value:
arm_max_f32(FFT_Output_f32, FFT_Length, &maxValue, &maxIndex);
}
}
My ADC is set to 620 Ksps and is initialised like this:
static void MX_ADC1_Init(void)
{
ADC_ChannelConfTypeDef sConfig;
/**Configure the global features of the ADC (Clock, Resolution, Data Alignment and number of conversion)
*/
hadc1.Instance = ADC1;
hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV2;
hadc1.Init.Resolution = ADC_RESOLUTION_12B;
hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;
hadc1.Init.ContinuousConvMode = DISABLE;
hadc1.Init.DiscontinuousConvMode = DISABLE;
hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_RISING;
hadc1.Init.ExternalTrigConv = ADC_EXTERNALTRIGCONV_T1_TRGO;
hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc1.Init.NbrOfConversion = 1;
hadc1.Init.DMAContinuousRequests = ENABLE;
hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
if (HAL_ADC_Init(&hadc1) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
/**Configure for the selected ADC regular channel its corresponding rank in the sequencer and its sample time.
*/
sConfig.Channel = ADC_CHANNEL_0;
sConfig.Rank = ADC_REGULAR_RANK_1;
sConfig.SamplingTime = ADC_SAMPLETIME_56CYCLES;
if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
}
And I belive the Prescaler and Period values for timer are correct as well for a 10us delay given that Timer 1 is connected to the ABP1 timer which runs at 108MHz according to CubeMX
static void MX_TIM1_Init(void)
{
TIM_ClockConfigTypeDef sClockSourceConfig;
TIM_MasterConfigTypeDef sMasterConfig;
htim1.Instance = TIM1;
htim1.Init.Prescaler = 0;
htim1.Init.CounterMode = TIM_COUNTERMODE_UP;
htim1.Init.Period = 1079; // APB1 clock is HCLK/2 for 100 Khz signal.
htim1.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
htim1.Init.RepetitionCounter = 0;
htim1.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_ENABLE;
if (HAL_TIM_Base_Init(&htim1) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
if (HAL_TIM_ConfigClockSource(&htim1, &sClockSourceConfig) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
sMasterConfig.MasterOutputTrigger = TIM_TRGO_UPDATE;
sMasterConfig.MasterOutputTrigger2 = TIM_TRGO2_UPDATE;
sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;
if (HAL_TIMEx_MasterConfigSynchronization(&htim1, &sMasterConfig) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
}
My DMA is also set to circular mode with High priority and FIFO disabled. I find that the buffer I'm using to store my ADC values is missing values from the adc for some of the elements in the array for the real part. My maxIndex value seems to be random and jumps all around the place. Modifying the DSPDEMO to use a signal from the ADCs as an input doesn't seem to help much either as my max index value is always shown to be in the 360 - 380thth element of a 1024 bin FFT output. which works out to be around 35 - 40 KHz.
I'm probably not doing something right with the timer. I would appreciate any help and if someone could point me in the right direction
